Northern Wallowas

Problemas de aludes

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Likely

  Tamaño

  1–2

  Strong to extreme winds have been recorded at all upper elevation wind stations in the last 48 hours.  The direction has mostly been out of the West/Southwest.  The wind has blown new snow into sensitive drifts along exposed terrain.  The new snow is sitting on a crust of variable thickness that was formed on many aspects earlier this week.  This created a solid bed surface on which newly formed wind slabs can easily be released.  

  The storm started cold and trended warmer over the last 24-48 hours.  This has created inverted or "upside-down" conditions within the new snow.  Dense and slabby conditions were the norm while travelling at all elevations yesterday.  Wind slabs that were formed with lighter snow on Wednesday have now been covered by a blanket of dense and heavy snow.  Wind slabs could be more reactive where they sit above lighter-density snow.

  Strong to Extreme wind speeds can create unfamiliar loading patterns- or it might have just blown all of our snow to Idaho!  Expect to find windslab development lower on slopes than you might commonly see.  

  Look for clues to wind loading patterns in the terrain: 

  • Dune-like features downwind of stripped locations
  • Snow surface textures that look rippled and stiff 
  • Note if your machine or boards are staying on top of a stiff and supportable slab of snow 
  • Cornice growth along ridgelines- wind slabs are often most sensitive downwind of corniced ridgelines
  • Shooting cracks/collapsing on the surface
  • Patterns of cross-loading on mid-slope terrain features.  

  The best riding and the least exposure today will be in wind-sheltered locations.  

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Likely

  Tamaño

  1–2

  As temperatures warm and rain falls on snow, the surface of the snowpack will continue to become weaker, and wet loose avalanches will likely develop in terrain steeper than 35 degrees.  Monitor the moisture of the surface snow.  Use small and inconsequential test slopes to determine the reactivity of the surface snow.  Terrain traps could enhance the consequences of even a small wet loose avalanche.  Avoid riding above cliffs, gullies, creeks, and benches if you are seeing reactive wet loose activity.  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Possible

  Tamaño

  2–3

  The Valentine's Day Buried Surface Hoar layer, along with weak faceted snow from the January Drought (buried on Feb 8), exists in the upper 3 feet of the snowpack.  While becoming less likely, If you trigger a slab avalanche on either or both of these fragile weak layers, you will likely produce a large to very large avalanche.   

  A new load of snow and wind-blown snow will challenge the weak layers in our snowpack.  It will be prudent to give steep, consequential avalanche terrain a wide berth until this storm passes.  

  Persistent Slab avalanches can release in surprising ways:

  • They can be much wider than expected 
  • They can break above you and pull into relatively gentle terrain.
  • Persistent slab avalanches can and will release on slopes that already have snowmachine or ski tracks. 
  • Although unlikely right now, you can trigger them remotely—from flat terrain below, above, and to the sides of steep slopes.  

  Specific terrain features that you should avoid: 

  • Rocky areas that are also convex rollovers- these areas may harbor a shallower snowpack and could be easier to trigger a persistent slab avalanche.
  • Slopes on the north half of the compass that are protected from the wind but are connected to larger open slopes that may have had previous wind loading.  

  If you have uncertainty in managing this avalanche problem, you are in good company.   The absence of obvious signs of instability, such as collapsing or whumphing of the snowpack, does not necessarily mean a slope is safe to ride.  Avoidance is our top (and our only) tool when it comes to dealing with a persistent slab.   Further slope scale investigation is warranted if you decide to commit to consequential terrain.